I think you're striving for a master-detail report style: Here's an idea
Try using a list data region, grouping by Account, and add your two tables within the list region. Here's a link that illustrates the technique:
http://jesborland.wordpress.com/2010/11/17/the-power-of-reporting-services-–-lists/
Also, here's a link to nesting data regions in SSRS:
http://msdn.microsoft.com/en-us/library/cc627449(v=sql.100).aspx
Lastly, one other link that might help:
http://technet.microsoft.com/en-us/library/dd239330(v=sql.105).aspx